Therapeutic results were analysed in 50 patients, including 17 with polymyositis (PM) and 30 with dermatomyositis (DM). All patients were treated with prednisone (Encorton, Polfa) and 47% of patients with PM and 73% with DM required combined treatment with prednisone and cytostatic agents, mostly with cyclophosphamide (Endoxan G.D.R.). Long-term treatment monitored with the clinical status led to remissions persisting after treatment discontinuation in 17.6% of PM patients and 24.2% of DM patients. In 64.7% of PM patients and 57.6% of DM patients regression of the clinical signs of the disease was achieved but these patients required further treatment. No information was obtained on 5 cases. Four DM patients died. The cumulative 17-year survival rate of PM patients was 100%, and that of DM patients was 78.8% . In 45 follow-up cases, the mortality was 8.9%. Side effects of the combined treatment included most frequently mucosal candidiasis (22.2%), transient leucopenia (14.8%) and recurrent respiratory tract infections (11.1%). In 5 cases liver biopsy was done and histological examination disclosed moderate fatty, glycogen and vacuolar degeneration of the hepatocytes. The statistical analysis of prognostic factors such as the diagnosis of PM or DM, sex, age at disease onset, disease duration till diagnosis establishing and beginning of treatment, fever, dysphagia, circulatory and respiratory changes, leucocytosis nad ESR at the beginning of the disease showed that sex (female), older age at disease onset and respiratory system changes may be accepted as poor prognosis factors.